An electric bell consists of an iron core, on which is wound a wire as a coil. One end of the coil is connected to one terminal of a battery, and the other end to a steel rod that acts like a spring for the hammer touching the screw contact. The other terminal of the battery is connected to the screw contact with a switch in the middle.
Working of an electric bell
Electric current flows through the coil when the switch is ON, and the iron core acts as an electromagnet. The iron core attracts the hammer towards it. The hammer hits the bell and produces a sound. The circuit breaks at the screw contact when the hammer moves towards the iron core. At this point, the iron core ceases to be an electromagnet. The hammer is pulled back to its original position due to the spring action of the steel rod, and then touches the contact again to complete the circuit. The circuit is completed and current flows through the coil again, and the hammer strikes the bell again. The process repeats itself and you hear a ringing sound since the hammer keeps hitting the bell, until the switch is released.

Basically the terms dilute and concentrated are used in reference to the amount of a solute that is dissolved in a given quantity of solvent. In dilute solutions, the amount of solute is less while that of solvent is more. On the other hand in concentrated solutions, the amount of solute is more while that of solvent is less.
So, concentrated acids are those in which have more amount of acid and less amount of water. The number of H⁺  ions in such solution is also high. Conversely, dilute acids are those in which amount of acid is less, but water is more. The number of H⁺  ions in such solutions is low.

1. Used oils and fats should not be poured into the sink which may choke the pipes. We should always throw oils and fats in the dustbin as in open drain the fats clog the soil pores and the filtration of water.
2. Many household chemicals like paints, motor oil, insecticides, etc. should not be allowed to go down as these are very toxic and harmful to both humans and microbes.
3. Used tealeaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin which may choke the drains as it do not allow the free flow of oxygen and thus hamper the degradation process by microorganisms.

Bases turn red litmus blue, so nature of ammonia is basic

Advantages of biogas :-
1. Biogas is eco-friendly 
2. Biogas generation reduces soil and water pollution 
3. Biogas generation produces organic fertilizer
4. It 's a simple and low-cost technology that encourages a circular economy 
5. healthy cooking alternative for developing areas
Disadvantage of biogas :-
1. few technological advancements
2. Contains impurities
3. effect on temperature on biogas production
4. Les suitable for dense metropolitian area

A metalloid is a type of chemical element which has properties in between, or that are a mixture of, those of metals and nonmetals. Silicon is a metalloid, sodium is a metal and chlorine is a non-metal.

• Sanitation and Disease

Many people in our country still do not have an access to proper sanitation facilities. They defecate in the open, on dry riverbeds, on railway tracks, near fields and many a time directly in water.

Poor sanitation and contaminated drinking water is the cause of a large number of diseases. Untreated human excreta is a health hazard and cause water pollution and soil pollution. When both the surface water and groundwater get polluted it becomes the most common route for water borne diseases like cholera, typhoid, polio, meningitis, hepatitis and dysentery.

• Alternative Arrangement of Sewage Disposal: In such places where sewage treatment plants are not accessible, alternative methods for sewage disposal are used. To improve sanitation, low cost onsite sewage disposal systems are being encouraged. For example - septic tanks, chemical toilets, composting pits. A septic tank is a highly efficient underground waste water treatment system. It is less expensive than other sewer systems and uses natural processes to treat the waste water. Some organizations offer hygienic on-site human waste disposal technology in which the toilets do not require scavenging. Excreta from the toilet seats flow through covered drains into a biogas plant and biogas is produced.

• Sanitation at Public Places: In our country a large number of fairs are organised periodically in which people participate. So, railway stations, bus depots, airports, hospitals are the busiest places where thousands of people visit daily. A large amount of waste is generated in such places which must be disposed of properly otherwise it will result into epidemics. The government has laid down certain standards of sanitation but, unfortunately, they are not strictly enforced. We should contribute in maintaining sanitation at public places.

There are some ways in which we can contribute in maintaining sanitation at public places like we should not scatter litter at public places.

We should play a keen role in keeping our environment clean and healthy. We must realise our responsibility in maintaining the water sources in a healthy state.

Respiration happens in amoeba through simple diffusion of gases. It lives in water which contains dissolved oxygen. The diffusion of gases takes place through its cell membrane. Through its thin cell membrane this oxygen diffuses into the body of amoeba and spreads into the whole body. This oxygen is used for respiration inside the Amoeba cell. The process of respiration produces carbon dioxide which diffuses out again through its thin cell membrane.

Electromagnets are made out of a coil of wire (wire curled in series). This is more effective in producing a magnetic field than just a wire running straight. This effect can be strengthened by winding a wire tightly around a powerful core, made of magnetic material, such as iron. The picture above shows a coil wound around an iron nail. On its own, the iron nail is not magnetic.

Drip irrigation is a advanced method of irrigation where the water is released drop by drop just near the roots of plants. 

It is considered advantageous over other methods of irrigation since it delivers water directly to the plant where it is required, i.e. the roots. It minimizes water loss through evaporation from surrounding soil. This makes it the most economical method of irrigation. It is highly stable for water deficient regions.